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Abstract:

The invention relates to foamed polyvinylidene tubular structures--and
particularly those for use as conduit. The tubular structures may be
corrugated, and are especially useful for fiber-optic plenum conduit. The
polyvinylidene foam may also be directly applied to fiber optic cable.

4. The tubular structure of claim 1, wherein said structure is corrugated.

5. The tubular structure of claim 1, wherein said composition further
comprises from 0.02 to 2 weight percent of one or more flame retardants,
based on the weight of said polyvinylidene fluoride.

6. The tubular structure of claim 1, further comprising at least one
additive selected from the group consisting of fillers, dyes, colorants
and impact modifiers.

7-9. (canceled)

10. A process for forming a foamed polyvinylidene fluoride tube,
comprising the steps of:a. admixing one or more polyvinylidene fluoride
resins with at least one foaming agent;b. extruding said admixture at a
temperature effective to activate the foaming agent to produce a foamed
tubular structure.

11. The process of claim 10, wherein said foaming agent is a liquid or
solid.

12. The process of claim 11, wherein said foaming agent is added at from 1
to 10 weight percent, based on the weight of polyvinylidne fluoride.

13. The process of claim 10, wherein said foaming agent is a gas, solid or
liquid admixed directly into the extruder.

14. The process of claim 10, further comprising the step of corrugating
said foamed tubular structure.

15-17. (canceled)

Description:

FIELD OF THE INVENTION

[0001]The invention relates to foamed polyvinylidene fluoride tubular
structures--especially those for use as conduit, and particularly for
plenum conduit. The tubular structures may be corrugated, and are
especially useful for fiber-optic plenum conduit. The polyvinylidene foam
may also be directly applied to fiber optic cable as primary insulation,
as a jacket or as a foamed support structure in the cable.

BACKGROUND OF THE INVENTION

[0002]Polyvinylidene Fluoride is commonly used to produce tube products
for wire and cable applications, as well as for jackets and primary
insulation on wire and cable products. Copper, fiber optic, and plenum
cables and conduit exist in large numbers in most commercial buildings.
In the case of tubular structures, a common product referred to as a
corrugated innerduct, is used for routing fiber optic cables in
buildings. The current product is a solid PVDF tube that contains
corrugations. Polyvinylidene fluoride (PVDF) is the preferred material
for conduit used in these plenum applications because of its inherent
toughness, inertness, and especially its flame and smoke resistance.
Other materials, such as polyvinyl chloride (PVC) and polyolefins, and
even other fluoropolymers do not have the same balance of properties that
PVDF provides.

[0003]One problem with PVDF, is the relatively high cost. The cost of a
PVDF conduit can be lowered by adding fillers, including inorganic
fluoride fillers, as described in U.S. patent application Ser. No.
11/158,235. Unfortunately the physical properties of the filled materials
are not as good as non-filled PVDF structures, tending to be stiffer and
have marginal crack resistance.

[0004]U.S. Pat. No. 4,322,260 described the use of
acrylonitrile/butadiene/styrene polymer foam as the insulation in
double-walled conduit structures. Foamed fluoropolymers mixtures of
ethylene/tetrafluoroethylene and ethylene/chlorotrifluoroethylene have
been used as an insulation directly on wire or cable, as described in
U.S. Pat. No. 5,770,819. U.S. Pat. No. 6,231,919 describes an advantage
using a solid or liquid blowing agent rather than gases for producing
foamed fluoropolymers wire coatings. The useful fluoropolymers are listed
as fluorinated ethylene-propylene, and perfluoroalkoxypolymers (such as
tetrafluoroethylene and perfluoropropylvinylether. None of these
references describe a foamed fluoropolymer conduit, and none describes
polyvinylidene fluoride foam.

[0005]A polyvinylidene fluoride foam is described in U.S. Pat. No.
7,081,216. The foam is produced by freezing a PVDF emulsion, followed by
thawing.

[0006]It has now been found that a polyvinylidene conduit can be formed
using foamed PVDF. The foamed conduit is lighter, more flexible, and less
expensive than solid PVDF conduit, while retaining good physical
properties and flame and smoke resistance.

SUMMARY OF THE INVENTION

[0007]The invention relates to foamed polyvinylfluoride tubular
structures, especially to those used as conduit or for jacketing of fiber
optic cable.

[0008]The invention also relates to a process for forming foamed
polyvinylfluoride tubular structures.

[0010]By "tubular structure" as used herein is meant a structure that is
much longer than it is thick, having a continuous passage through the
structure in the length-wise direction. The structure may be of any
cross-sectional shape, including a preferred circular shape, and may also
be corrugated (having ridges running in the direction of the tube
length). The passage in the middle of the tube may contain empty space;
be partially filled with other components (such as fiber optic cable or
copper wires); or be completely filled by a fiber optic cable or other
structure, in which the PVDF foam is directly in contact with the other
structure.

[0011]The term "polyvinylidene fluoride", as used herein, includes both
normally solid, high molecular weight homopolymers and copolymers within
its meaning. Such copolymers include those containing at least 50 mole
percent of vinylidene fluoride copolymerized with at least one comonomer
selected from the group consisting of tetrafluoroethylene,
trifluoroethylene, chlorotrifluoroethylene, hexafluoropropene, vinyl
fluoride, pentafluoropropene, perfluoromethyl vinyl ether,
perfluoropropyl vinyl ether and any other monomer that would readily
copolymerize with vinylidene fluoride. Particularly preferred are
copolymers composed of from at least about 70 and up to 99 mole percent
vinylidene fluoride, and correspondingly from 1 to 30 percent
tetrafluoroethylene, about 70 to 99 percent vinylidene fluoride and 1 to
30 percent hexafluoropropene; and about 70 to 99 mole percent vinylidene
fluoride and 1 to 30 mole percent trifluoroethylene. Terpolymers of
vinylidene fluoride, hexafluoropropene and tetrafluoroethylene and
terpolymers of vinylidene fluoride, trifluoroethylene and
tetrafluoroethylene are also representatives of the class of vinylidene
fluoride copolymers which can be used. The polyvinylidene fluoride resin
used in the invention may also be a mixture of one or more different
polyvinylidene fluoride resins.

[0012]The molecular weight and composition of the polyvinylidene fluoride
to obtain the desired processability and final product properties.

[0013]The polyvinylidene fluoride is generally made by a suspension,
emulsion, or supercritical CO2 process.

[0014]The polyvinyl fluoride polymer is formed into a foam by the addition
of a foaming agent. The foaming agent may be a gas (such as Freon or
nitrogen), or a solid or liquid foaming agent. Generally the foaming
agent is added into an extruder system, the foam forming immediately upon
the exodus of the mixture from the extruder.

[0015]In one embodiment, a foam concentrate is added to the polyvinylidene
fluoride softened resin at a level of from 1 to 10 percent by weight, and
preferably from 2 to 5 percent by weight, based on the weight of the
polyvinylidene fluoride.

[0016]The foam produced reduces the density of the final product by at
least 5 percent.

[0017]In addition to the polyvinylidene fluoride resin and foaming agent,
the composition of the invention may further contain other additives.
Examples of other additives include, but are not limited to: flame
retardants, dyes or colorants, fillers, impact modifiers, and other
polymers. Flame retardants include, but are not limited to, tungstates,
molybdates and silicates. An especially preferred flame retardant is
calcium tungstate. The flame retardants are generally added to the
composition at a level of from 0.02 to 2.0 weight percent, based on the
weight of polyvinylidene fluoride. In a preferred embodiment, the foamed
PVDF meets the flame and smoke requirements as defined in the Steiner
Tunnel test method, UL 2024. The foamed conduit of the invention can meet
the plenum requirements specified in NFPA-262.

[0018]Dyes and colorants may be added as color concentrates at levels
between 1 and 5% based on the total amount of polymer. Fillers, at levels
of up to 40 percent by weight, based in the polyvinylidene fluoride may
be added. The fillers include inorganic fillers, polymeric fillers, and
mixtures thereof. The addition of filler can help reduce the cost of the
composition, though some loss in performance properties will result.
Inorganic fillers include, but are not limited to, zinc oxide, calcium
carbonate, and inorganic fluorides such as calcium fluoride. Polymer
additives include acrylics and other polymers compatible with PVDF.
Processing aids, such as polytetrafluoroethylene (PTFE), may be added to
optimize processing conditions, such as a reduction in the coefficient of
friction.

[0019]The foamed structures of the invention are generally formed in an
extrusion or coextrusion process.

[0020]In a preferred embodiment, the foamed tubular polyvinylidene
fluoride composition is formed into a conduit. In a more preferred
embodiment, the conduit is formed into a corregated conduit by the
application of vacuum, pressure or both. Corregation provides a more
flexible tubular structure, with improved structural integrity.

[0021]In one embodiment of the invention, a solid inner liner is formed
into a tube, onto which the foamed polyvinylidene fluoride composition is
extruded. The solid inner liner could be a polymer, such as solid PVDF,
polyvinylidene chloride (PVC), or polyethylene (PE). The inner liner
might also consist of a metal sheath, such as, but not limited to steel
and aluminum, forming an armored conduit. In this case armored cable is
produced by a process where a metal is wound over the cable in a manner
that creates an interlocking outer metal tube over the cable. The PVDF
and other additives are blended together, and a foaming agent either
added to the blend, or in the case of a gas, directly injected into the
extruder. Upon exiting the extruder, the gases from the foaming agent
expand the PVDF composition to form a foam over the armored cable.

[0022]Typically, the foamed tubular structure of the invention has an
outside diameter of from 10 millimeters (0.25 inches) to 20 centimeters
(8 inches). Wall thickness can range from 0.005 inches up to 0.050
inches.

[0024]The tubular structure is useful as a conduit of electrical and fiber
optic cable, as a replacement for current solid-walled PVDF conduit. The
foamed conduit may be referred to as a plenum cable, raceway, innerduct,
or similar designation. Additionally, the foamed PVDF can be applied
directly to optical cable or onto other substrates as a tough,
low-density, flexible coating or insulation.

EXAMPLES

[0025]A foam at a level of 3 percent is blended into KYNAR3120-15 and
extruded using a barrel temperature set up to 460° F. and with die
and tooling set at temperatures as high as 480° F. (or at
temperatures adequate to activate the foaming agent to produce the
foaming action). The extruder provides melt into a "melt tube" that is
designed to introduce material into commercial tube corrugators. The melt
tube may need to be specially designed to have the pressure drop
primarily focused at the end of the melt tube. Heat may also be required
on the melt tube to promote foaming of the KYNAR resin. The KYNAR foams
as it exits the melt tube and expands as the gasses created by the
foaming concentrate are released. The foam tube is taken within the
corrugators and with the use of vacuum, pressure or both, the tube is
formed into a corrugated tube product. The final product in the form of a
corrugated tube exits the corrugators and is wound up on spools in
preparation for shipment. The product may contain a colorant such as
provided by an orange color concentrate to produce the final product.

Patent applications by James J. Henry, Downingtown, PA US

Patent applications by Saeid Zerafati, Villanova, PA US

Patent applications by Sean M. Stabler, Montoursville, PA US

Patent applications in class Foam or porous material containing

Patent applications in all subclasses Foam or porous material containing